1. Field
The present disclosure relates generally to noise filtering. More specifically the present disclosure relates to filtering in class-G/H amplifier circuits for headphones to avoid de-sensing/spurs of the FM receiver band.
2. Background
Headphones may be used in conjunction with wireless portable communication devices, as well as elsewhere. In a conventional headphone power amplifier system the coder-decoder (codec) charge-pump tones may fall in the FM band, which may need filtering to avoid de-sense of the FM receiver. A combination of ferrite beads (FB) plus capacitor offers low cost filtering. However, poor ferrite bead properties pose a difficult trade-off between high linearity audio reproduction and good FM reception. The filtering solution typically needs substantially sized components; however, very few ferrite beads in the market meet both audio and FM requirements.
There is a need to improve off chip filtering requirements for codec immunity to FM interference, reduce component size, and relax specifications for ferrite bead selection, i.e., to allow for greater flexibility in component sourcing.